Most conventional firearms rely on rapidly-expanding gasses created by rapid or explosive combustion of a material such as gunpowder to drive a projectile through a barrel and towards a target. This process is somewhat inefficient: not all of the energy in the explosion can be transferred to the projectile. However, some firearms make use of a portion of the energy to operate other mechanisms needed by the firearm. For example, semi-automatic and automatic firearms use a portion of the gas pressure to cycle the action, ejecting the spent cartridge and loading the next round. The trigger mechanism is also re-armed (and in an automatic firearm, the next round is fired if the trigger is still engaged).
Spent shells typically leave the ejection port with a fair amount of energy and fly some distance from the gun. In addition, since they are often oddly shaped and balanced, and made of a hard, springy material such as brass, they bounce and roll randomly, coming to rest over an inconveniently large area. This makes recovery of the shells for cleanup and/or reloading more difficult, particularly when a large number of rounds are fired in a short period of time (such as during target practice).
Prior-art methods to capture and/or collect ejected brass typically attach a bag or other receptacle to the gun (e.g., U.S. Pat. No. 4,166,333 to Kratzer, U.S. Pat. No. 4,715,141 to Kohnke; U.S. Patent Application Publication No. 2012/0023803 by Taylor), or place it on a stand nearby, with an opening positioned and sized to catch shells in flight (U.S. Pat. No. 3,658,241 to Pistocchi). However, these approaches are suboptimal because they interfere with the normal operation of the gun as the weight of collected brass increases, or they require that the shooter remain near the collecting bag so that ejected shells travel into the opening. New approaches for controlling ejected firearm shells may be of significant value in this field.